The amount of water available to a country depends on the rainfall it receives and the net result of water flows to and from neighbouring countries through sources such as rivers and aquifers. Water availability varies both seasonally and over longer periods in response to changes in climate. It also varies spatially between countries and regions, some of which have plentiful supplies while others suffer shortages or even droughts.

Globally, there is enough water to meet all our needs. In Europe, for example, up to 8800 litres of water is available for each European inhabitant per day (3200m³/year), but only 1800 litres (660m³) is abstracted. The problem is that this water is distributed unevenly, meaning that while some regions such as western Norway have access to lots of water, others, such as southern and central Spain, suffer shortages. Water scarcity is commonly defined as a situation where water availability in a country or in a region is below 2700 litres per person per day (representing 1000m³/year). However, many regions in the world experience much more severe scarcity, living with less than 1400 litres per person per day (500m³/year), which could be considered severe water scarcity. According to UNESCO more than 1 billion people live in areas where water is physically scarce and this figure is predicted to rise in the coming years. http://www.eea.europa.eu/data-and-maps/figures/annual-water-availability-per-person

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